Cable with circuitry for asserting stored cable data or other information to an external device or user

ABSTRACT

A cable including circuitry for asserting information to a user or external device and a system including such a cable. The cable can include conductors, a memory storing cable data, and circuitry configured to respond to a request received on at least one of the conductors by accessing at least some of the cable data and asserting the accessed data serially to at least one of the conductors (e.g., for transmission to an external device). Other aspects of the invention are methods for accessing cable data stored in a cable and optionally using the data (e.g., to implement equalization). The cable data can be indicative of all or some of cable type, grade, speed, length, and impedance, a date code, a frequency-dependent attenuation table, far-end crosstalk and EMI-related coefficients, common mode radiation, intra pair skew, and other information. The cable can include a radiation-emitting element and circuitry for generating driving signals for causing the radiation-emitting element to produce an appropriate color, brightness, and/or blinking pattern.

FIELD OF THE INVENTION

The invention pertains to a cable for connecting a transmitter to areceiver (e.g., to implement a serial link over which video and otherdata are transmitted from the transmitter to the receiver). The cableincludes a memory that stores cable data and/or circuitry for assertinginformation to a user (e.g., by emitting radiation) or to an externaldevice (e.g., a transmitter or receiver coupled to the cable). Inpreferred embodiments, the invention is a cable including a memorystoring cable data and a serial device for asserting the cable data inserial fashion to an external device coupled to the cable.

BACKGROUND OF THE INVENTION

The term “transmitter” is used herein in a broad sense to denote anydevice capable of transmitting data over a serial link or other link,and optionally also capable of performing additional functions which caninclude encoding and/or encrypting the data to be transmitted. The term“receiver” is used herein in a broad sense to denote any device capableof receiving data that has been transmitted over a serial link or otherlink, and optionally also capable of performing additional functions,which can include decoding and/or decryption of the received data, andother operations related to decoding, reception, or decryption of thereceived data. For example, the term receiver can denote a transceiverthat performs the functions of a transmitter as well as the functions ofa receiver.

The expression “serial link” is used herein to denote a serial link(having any number of channels) or a channel of a serial link, where theterm “channel” of a serial link denotes a portion of the link that isemployed to transmit data in serial fashion (e.g., a conductor orconductor pair between a transmitter and receiver over which data aretransmitted serially, either differentially or in single-ended fashion).

There are various, well-known serial links for transmitting video dataand other data. One conventional serial link is known as a transitionminimized differential signaling interface (“TMDS” link). This link isused primarily for high-speed transmission of video data from a set-topbox to a television, and also for high-speed transmission of video datafrom a host processor (e.g., a personal computer) to a monitor. Amongthe characteristics of a TMDS link are the following:

1. video data are encoded and then transmitted as encoded words (each8-bit word of digital video data is converted to an encoded 10-bit wordbefore transmission);

2. the encoded video data and a video clock signal are transmitted asdifferential signals (the video clock and encoded video data aretransmitted as differential signals over conductor pairs without thepresence of a ground line); and

3. three conductor pairs are employed to transmit the encoded video, anda fourth conductor pair is employed to transmit the video clock signal.

Another serial link is the “High Definition Multimedia Interface”interface (“HDMI” link) developed Silicon Image, Inc., MatsushitaElectric, Royal Philips Electronics, Sony Corporation, ThomsonMultimedia, Toshiba Corporation, and Hitachi. It has been proposed totransmit encrypted video and audio data over an HDMI link.

Another serial link is the “Digital Video Interface” (“DVI” link)adopted by the Digital Display Working Group. It has been proposed touse the cryptographic protocol known as the “High-bandwidth DigitalContent Protection” (“HDCP”) protocol to encrypt digital video data tobe transmitted over a DVI link, and to decrypt the encrypted video dataat the DVI receiver. A DVI link can be implemented to include two TMDSlinks (which share a common conductor pair for transmitting a videoclock signal) or one TMDS link, as well as additional control linesbetween the transmitter and receiver. We shall describe a DVI link (thatincludes one TMDS link) with reference to FIG. 1. The DVI link of FIG. 1includes transmitter 1, receiver 3, and the following conductors betweenthe transmitter and receiver: four conductor pairs (Channel 0, Channel1, and Channel 2 for video data, and Channel C for a video clocksignal), Display Data Channel (“DDC”) lines for bidirectionalcommunication between the transmitter and a monitor associated with thereceiver in accordance with the conventional Display Data Channelstandard (the Video Electronics Standard Association's “Display DataChannel Standard,” Version 2, Rev. 0, dated Apr. 9, 1996), a Hot PlugDetect (HPD) line (on which the monitor transmits a signal that enablesa processor associated with the transmitter to identify the monitor'spresence), Analog lines (for transmitting analog video to the receiver),and Power lines (for providing DC power to the receiver and a monitorassociated with the receiver). The Display Data Channel standardspecifies a protocol for bidirectional communication between atransmitter and a monitor associated with a receiver, includingtransmission by the monitor of Extended Display Identification (“EDID”)data that specifies various characteristics of the monitor, andtransmission by the transmitter of control signals for the monitor.Transmitter 1 includes three identical encoder/serializer units (units2, 4, and 5) and additional circuitry (not shown). Receiver 3 includesthree identical recovery/decoder units (units 8, 10, and 12) andinter-channel alignment circuitry 14 connected as shown, and additionalcircuitry (not shown).

As shown in FIG. 1, circuit 2 encodes the data to be transmitted overChannel 0, and serializes the encoded bits. Similarly, circuit 4 encodesthe data to be transmitted over Channel 1 (and serializes the encodedbits), and circuit 6 encodes the data to be. transmitted over Channel 2(and serializes the encoded bits). Each of circuits 2, 4, and 6 respondsto a control signal (an active high binary control signal referred to asa “data enable” or “DE” signal) by selectively encoding either digitalvideo words (in response to DE having a high value) or a control orsynchronization signal pair (in response to DE having a low value). Eachof encoders 2, 4, and 6 receives a different pair of control orsynchronization signals: encoder 2 receives horizontal and verticalsynchronization signals (HSYNC and VSYNC); encoder 4 receives controlbits CTL0 and CTL1; and encoder 6 receives control bits CTL2 and CTL3.Thus, each of encoders 2, 4, and 6 generates in-band words indicative ofvideo data (in response to DE having a high value), encoder 2 generatesout-of-band words indicative of the values of HSYNC and VSYNC (inresponse to DE having a low value), encoder 4 generates out-of-bandwords indicative of the values of CTL0 and CTL1 (in response to DEhaving a low value), and encoder 6 generates out-of-band wordsindicative of the values of CTL2 and CTL3 (in response to DE having alow value). In response to DE having a low value, each of encoders 4 and6 generates one of four specific out-of-band words indicative of thevalues 00, 01, 10, or 11, respectively, of control bits CTL0 and CTL1(or CTL2 and CTL3).

In operation of the FIG. 1 system, a cable comprising connectors 20 and21 and conductors (wires) 22 is connected between transmitter 1 andreceiver 3. Conductors 22 include a conductor pair for transmittingserialized data over Channel 0 from encoder 2 to decoder 8, a conductorpair for transmitting serialized data over Channel 1 from encoder 4 todecoder 10, a conductor pair-for transmitting serialized data overChannel 2 from encoder 6 to decoder 12, and a conductor pair fortransmitting a video clock over Channel C from transmitter 1 to receiver3. Conductors 22 also include wires for the DDC channel (which can beused for bidirectional I2C communication between transmitter 1 andreceiver 3), a Hot Plug Detect (HPD) line, “Analog” lines for analogvideo transmission from transmitter 1 to receiver 3, and “Power” linesfor provision of power from transmitter 1 to a receiver 3.

Other serial links include the set of serial links known as Low VoltageDifferential Signaling (“LVDS”) links (e.g., “LDI,” the LVDS DisplayInterface), each of which satisfies the TIA/EIA-644 standard or theIEEE-1596.3 standard, ethernet links, fiberchannel links, serial ATAlinks used by disk drives, and others.

During high-speed data transmission over a cable, the cable itselfintroduces losses and dispersion which reduce the signal quality at thereceiver end. High-speed serial communication makes it possible totransfer high-speed data over a single conductor or conductor pair.However, as one or both of the frequency of transmitted signal and thecable length increases, the distortion due to frequency dependent delayand attenuation can make the eye at the receiver almost unusable. Also,handling of the cable itself becomes difficult for typical users inconsumer applications.

Frequency dependent attenuation not only attenuates signals but alsogenerates dispersion. These artifacts increase the chance of falsedetection of received signals. The most important parameter for thereceiver is the eye opening at the receiver. A larger eye opening iscorrelated with better signal quality. Major sources of signaldistortion are frequency dependent attenuation, imperfect impedancematching, far end cross talk and EMI. For relatively low frequencysignals, various signal processing techniques (e.g., adaptiveequalization) have been used to compensate for signal distortion.However, for higher frequency signals, especially those indicative of anNRZ (non return to zero) data stream, equalization becomes moredifficult if the cable characteristics are not well defined or known. Byusing sophisticated methods, cable characteristics can be deduced usingcircuitry in a transmitter and/or receiver (with the cable connectedbetween the transmitter and receiver) but this requires complexhandshaking and signal processing circuitry.

Transmission of signals indicative of data (e.g., signals indicative ofvideo or audio data) to a receiver over a cable degrades the data, forexample by introducing time delay error (sometimes referred to asjitter) to the data. In effect, the cable applies a filter (sometimesreferred to as a “cable filter”) to the signals during propagation overthe cable. The cable filter can cause inter-symbol interference (ISI).

Equalization is the application of an inverted version of a cable filterto signals received after propagation over a link. The function of anequalization filter (sometimes referred to as an “equalizer”) is tocompensate for, and preferably cancel, the cable filter. A transmittercan implement “pre-emphasis” equalization by applying relatively greateramplification to some data values of a sequence of data values to betransmitted, and relatively less amplification to other data values ofthe sequence. A receiver can also implement an equalization filter.

In a system for transmitting data over a cable from a transmitter to areceiver, either or both of the transmitter and receiver can performequalization. In many such systems, the user can couple any of a varietyof cables between the transmitter and receiver and can swap one cablefor another (e.g., one of different length) when desired. A set ofequalization parameters suitable for use with one cable would often beunsuitable for use when this cable is replaced by another cable (e.g., amuch shorter or much longer cable). Until the present invention it hadbeen time-consuming and/or expensive to determine an optimal (orsuitable) set of equalization parameters for an equalization filter in atransmitter or receiver of such a system (for example, sincecharacterization of cable properties had required complex handshakingand signal processing circuitry, as noted above).

SUMMARY OF THE INVENTION

In a class of embodiments, the invention is a cable including a memorywhich stores cable data (indicative of at least one characteristic ofthe cable), a conductor set, and circuitry coupled to at least oneconductor of the conductor set and configured to respond to a, cabledata request received on at least one conductor of the conductor set(e.g., from a transmitter or other external device coupled to the cable)by accessing at least some of the stored cable data and asserting theaccessed data serially to at least one conductor of the conductor set(e.g., for transmission to an external device coupled to the cable). Theconductor set includes at least one conductor and typically two or moreconductors. The memory and the circuitry can be included in a serialdevice, or the circuitry can be included in a serial device and thememory can be an element distinct from and coupled to the serial device.An external device can use the cable data to implement equalization orotherwise to mitigate adverse effects due to cable-introduced losses anddispersion. For example, in typical embodiments the cable is coupledbetween a transmitter and a receiver, and a serial device in the cableis configured to assert cable data (requested by the transmitter)serially to the transmitter. The transmitter can then use the cable datato implement equalization. For example, the transmitter can use thecable data to choose optimum pre-emphasis values for pre-emphasis ofcontent data (data to be transmitted over the cable to the receiver),and/or to set (or cause the receiver to set) parameters for equalizationcircuitry and/or termination circuitry in the receiver. For example, thetransmitter could transmit at least some of the cable data (or signalsgenerated in response to the cable data) to the receiver for use by thereceiver in setting equalization parameters.

In another class of embodiments, the inventive cable includes circuitryfor asserting information (e.g., by displaying an indication of cabledata stored within the cable) to a user or external device (e.g., atransmitter or receiver coupled to the cable). In some such embodiments,the cable is configured to implement at least one cable guide functionby asserting cable guide information, for example, by displaying anindication of the cable guide information. The cable guide informationcan indicate what type of device a free end of the cable should beconnected to when the other end of the cable has been connected to adevice of known type. Circuitry within the cable can cause the cable todisplay an indication of the type of device to which the free end shouldbe connected when the circuitry has determined that the other end of thecable has been connected to a device of known type.

In typical embodiments, the inventive cable includes two connectors, aconductor set is coupled between the connectors, and a serial device isincluded in one of the connectors (or in each of both connectors) or isdistributed over both connectors. Cable data can be stored in a memorythat is included in one said serial device, or can be stored in at leastone memory that is distinct from but coupled to at least one said serialdevice. The serial device is coupled to a “cable data channel” (one ormore conductors of the conductor set, and typically one or twoconductors of the conductor set) and is configured to respond to arequest for cable data (e.g., a request received over the cable datachannel from a transmitter or other device external to the cable butcoupled to the cable data channel) by asserting cable data (stored inthe memory) over the cable data channel (e.g., to an external device).Typically, a serial bus controller in a transmitter (or other deviceexternal to the cable) controls communication over the cable datachannel. A control mechanism (for accessing cable data from the cableand using the accessed cable data) can be implemented as software (e.g.,as a software device driver) and can be programmed into a serial buscontroller in a transmitter (or other device external to the cable).

In typical use, the cable is coupled between a transmitter and receiverand a cable data channel of the cable is employed for relativelylow-speed, serial communication between the transmitter and receiverwhile data (e.g., video and/or audio data) are transmitted (from thetransmitter to the receiver) at a higher data rate over other conductorsof the cable's conductor set. As one example, the transmitter andreceiver are coupled via a DVI link, the Display Data Channel (“DDC”)lines of the DVI link are the cable data channel. Serial communicationover the cable data channel (between an external device and a serialdevice in the cable) can occur at a relatively slow speed, and if so,the serial device can be implemented more simply than if the serialcommunication must occur at a high data rate.

In typical embodiments, the serial device of the inventive cable is anI2C interface and includes a ROM which stores the cable data. Typically,the cable data are indicative of all or some of the cable manufacturer,the cable type and/or cable class, a date code, a frequency-dependentattenuation table, FEXT (far-end crosstalk) coefficients, cableimpedance, cable length (electrical length), cable grade, EMI-relatedcoefficients, common mode radiation, cable speed, intra pair skew, andother information. The ROM can be a mask ROM in which the cablemanufacturer writes cable data regarding the specific cable or cablemodel, or it can be a PROM which is programmed at the manufacturingstage with cable data regarding the specific cable or cable model.Alternatively, the cable data are stored in another type of ROM or othermemory. For example the memory (which stores the cable data) can be ananalog memory implemented as a resistor or resistor network, or it canbe another analog memory.

In some embodiments, the cable includes at least one LED (or otherradiation-emitting element) coupled to and driven by circuitry (e.g., aserial device) in the cable. In some embodiments, the cable has twoserial devices (e.g., one in a connector at one end of the cable andanother in a connector at the cable's other end) and two LEDs (or otherradiation-emitting elements), one driven by each serial device.Preferably, each serial device is configured to generate driving signalsin response to signals (which can be, but are not necessarily, commands)from an external device (e.g., by translating commands received over thecable data channel from a serial device master in a transmitter coupledto the cable, where the serial device master controls communication overthe cable data channel). The driving signals can cause a LED (or otherradiation-emitting element) to produce an appropriate color, brightness,and/or blinking pattern. The serial device can cause an LED (or otherradiation-emitting element) to emit radiation indicative of connectionstatus (e.g., whether the cable is properly connected to a transmitterand/or receiver), or number of errors, or other information (e.g., otherinformation for diagnosing signal transmission or cable status).

In a system including an embodiment of the inventive cable coupledbetween a transmitter and receiver, one or both of the transmitter andreceiver can include an LED (or other radiation-emitting element) andcircuitry for driving the radiation-emitting element. Radiation emittedfrom each radiation-emitting element can guide cable installation orcheckup of connections such as by indicating connection status and/orother information using color, brightness or blinking pattern.

Radiation emitted from each radiation-emitting element (in the inventivecable and/or an external device coupled thereto) can also indicate thetype of signal (or types of signals) being transmitted through the cable(e.g., a digital signal, content protected signal, or audio signal), orspecific signal activities, for example, using color, brightness andblinking pattern.

In some embodiments, cable data stored in the inventive cable includedata indicative of whether the cable is a secure cable (one over whichthe transmitter can securely transmit encrypted data). In someembodiments, the cable stores a cryptographic key set, and a serialdevice in the cable is configured to execute a verification operationwith a transmitter in which the transmitter and serial device identifythemselves (this step typically includes an exchange of keys) and thetransmitter determines whether the cable is a secure digital cable. In asystem including one of the latter embodiments of the inventive cable,the transmitter would typically also perform a verification operationwith the receiver. Upon successful completion of verification operationswith both the receiver and a serial device in the cable, the transmitterwould transmit encrypted data to the cable, and the encrypted data wouldpropagate through the cable to the receiver and undergo decryption inthe receiver. For example, if each of the transmitter and receiverincludes a cipher engine and is configured to operate in accordance withthe HDCP protocol, each of the transmitter, receiver, and cable couldstore an HDCP key set. The HDCP key set stored in the transmitter wouldinclude at least some keys unique to the transmitter (or to a smallnumber of devices including the transmitter), the HDCP key set stored inthe receiver. would include at least some keys unique to the receiver(or to a small number of devices including the receiver), and the HDCPkey set stored in the cable would include at least some keys unique tothe cable (or to a small number of devices including the cable).

In preferred embodiments, the inventive cable is configured forhigh-speed transmission of binary signals.

In a class of embodiments, the invention is a system including anyembodiment of the inventive cable and a transmitter and receiver coupledto the cable. In other embodiments, the invention is a method foraccessing cable data stored in any embodiment of the inventive cableand/or using cable data accessed from a memory of any embodiment of theinventive cable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional system for transmitting dataover a DVI link (that includes one TMDS link). The system includes atransmitter, a receiver, and a cable between the transmitter andreceiver.

FIG. 2 is a block diagram of a transmitter, a receiver, and anembodiment of the inventive cable between the transmitter and receiver.

FIG. 3 is a block diagram of a transmitter, a receiver, and anotherembodiment of the inventive cable (including equalization circuitry)between the transmitter and receiver.

FIG. 4 is a block diagram of a transmitter, a receiver, and anotherembodiment of the inventive cable (including two serial devices, eachcoupled to an LED) between the transmitter and receiver.

FIG. 5 is a block diagram of a transmitter, a receiver, and anotherembodiment of the inventive cable between the transmitter and receiver,in which each of the transmitter and receiver includes a cipher engine.

FIG. 6 is a block diagram of a transmitter, a receiver, and anotherembodiment of the inventive cable between the transmitter and receiver.

FIG. 7 is a block diagram of a transmitter, a receiver, and anotherembodiment of the inventive cable between the transmitter and receiver.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In a class of embodiments, the invention is a cable which stores cabledata, and includes a conductor set (at least one conductor, andtypically two or more conductors) for transmitting data between atransmitter and a receiver coupled to the cable, and a serial device forasserting cable data to an external device (e.g., the transmitter)coupled to the cable. At least one conductor of the conductor set isemployed as a “cable data channel” over which the serial devicetransmits cable data serially to an external device (e.g., thetransmitter) coupled to the cable. The serial device is coupled to thecable data channel and configured to respond to a request for cable data(from the transmitter or other device external to the cable but coupledto the cable data channel) by asserting cable data over the cable datachannel to the external device.

In preferred embodiments, the inventive cable includes a read-onlymemory (ROM) which stores the cable data. In other embodiments, theinventive cable includes a memory other than a ROM which stores thecable data. For example, in some embodiments, the inventive cableincludes an analog memory. For example, the analog memory can beimplemented as a resistor or resistor network which stores cable data inthe sense that when the cable is connected to a device, analog circuitrywithin the device is coupled to the analog memory, and the analogcircuitry determines (reads) the cable data by measuring or generating acurrent or voltage (or other electrical signal) indicative of the cabledata, where the electrical signal is determined by a resistance (orratio of resistances) in turn determined by the analog memory.

The expression “serial device” is used herein to denote a device capableof communication over a serial link with another device (e.g., atransmitter or receiver). In a class of embodiments (e.g., embodimentsin which the inventive cable implements a DVI link between a transmitterand a receiver), the cable's “serial device” includes interfacecircuitry coupled and configured for I2C communication with an I2Cmaster device within the transmitter (e.g., I2C communication with anI2C master device over the DDC channel of a DVI link). Such interfacecircuitry would implement an I2C slave protocol to assert (to thetransmitter) cable data from a ROM coupled to the interface circuitry,in response to I2C control bits received from the transmitter.

In preferred embodiments, video data (and/or audio data and/or otherdata) are transmitted serially over a first subset of the conductors ofthe conductor set, and a second subset of the conductors comprises thecable data channel. Typically, the second subset is distinct from thefirst subset, but alternatively the second subset includes at least oneconductor of the first subset.

In other embodiments, video data (and/or audio data and/or other data)are transmitted in parallel fashion over a first subset of theconductors of the conductor set, and a second subset of the conductorscomprises the cable data channel (over which cable data are transmittedserially to a device external to the cable). Typically, the secondsubset is distinct from the first subset, but alternatively the secondsubset includes at least one conductor of the first subset.

Embodiments of the inventive cable will be described with reference toFIGS. 2, 3, 4, and 5. The system of each of FIGS. 2, 3, 4, and 5includes a transmitter, a receiver, and a DVI link between thetransmitter and receiver. Cable 32 in FIG. 2 includes conductor set 35which includes all conductors needed to implement a DVI link betweentransmitter 31 and receiver 33. Connector 34 of cable 32 is configuredto be coupled to transmitter 31 so as to couple each conductor of set 35to a corresponding terminal of transmitter 31, and connector 36 of cable32 is configured to be coupled to receiver 33 so as to couple the otherend of each conductor of set 35 to a corresponding terminal of receiver33.

Cable 42 in FIG. 3 includes conductor set 45 which includes allconductors needed to implement a DVI link between transmitter 41 andreceiver 43. Connector 44 of cable 42 is configured to be coupled totransmitter 41 so as to couple each conductor of set 45 to acorresponding terminal of transmitter 41, and connector 46 of cable 42is configured to be coupled to receiver 43 so as to couple the other endof each conductor of set 45 to a corresponding terminal of receiver 43.

Similarly, cable 52 in FIG. 4 includes conductor set 55 which includesall conductors needed to implement a DVI link between transmitter 51 andreceiver 53. Connector 54 of cable 52 is configured to be coupled totransmitter 51 so as to couple each conductor of set 55 to acorresponding terminal of transmitter 51, and connector 56 of cable 52is configured to be coupled to receiver 53 so as to couple the other endof each conductor of set 55 to a corresponding terminal of receiver 53.

Each of conductor sets 35, 45, and 55 includes three conductor pairs(labeled “Red,” “Green,” and “Blue”) for transmitting high-speed binaryNRZ data (typically video data, or video and audio data), and aconductor pair (labeled “Clock”) for transmitting a clock (a pixelclock) for such data. Each of conductor sets 35, 45, and 55 alsoincludes conductors (labeled “DDC CLK” and “DDC DATA”) whichrespectively comprise the DDC channel of the DVI link of FIG. 2, FIG. 3,and FIG. 4. The DDC channel of FIG. 2 is for bidirectional communication(at relatively low speed) between transmitter 31 and receiver 33, theDDC channel of FIG. 3 is for bidirectional communication (at relativelylow speed) between transmitter 41 and receiver 43, and the DDC channelof FIG. 4 is for bidirectional communication (at relatively low speed)between transmitter 51 and receiver 53. The DDC channel of each DVI linkcan also be used for sharing HDCP keys in the case that the relevanttransmitter/receiver pair is configured to implement the HDCP protocol.

Each of conductor sets 35, 45, and 55 also includes DDC Power lines(labeled “VCC” and “GND”) and can include other conductors (not shown).Serial device master 38 (connected as shown in transmitter 31) controlsserial communication (in accordance with the I2C protocol) over the DDCchannel of the DVI link of FIG. 2 with each of serial device 39(connected as shown in receiver 33) and serial device 37 (connected asshown in connector 36 of cable 32. Serial device master 48 (connected asshown in transmitter 41) controls serial communication (in accordancewith the I2C protocol) over the DDC channel of the DVI link of FIG. 3with each of serial device 49 (connected as shown in receiver 43) andserial device 47 (connected as shown in connector 46 of cable 42. Serialdevice master 58 (connected as shown in transmitter 51) controls serialcommunication (in accordance with the I2C protocol) over the DDC channelof the DVI link of FIG. 4 with each of serial device 59 (connected asshown in receiver 53), serial device 60 (connected as shown in connector54 of cable 52), and serial device 61 (connected as shown in connector56,of cable 52). Each of serial devices 37, 39, 47, 49, 59, 60, and 61includes an I2C interface.

Serial device 37 includes memory 37A which stores cable data inaccordance with the invention. In preferred implementations, memory 37Ais a ROM (either a mask ROM in which the cable manufacturer writes thecable data, or a PROM which is programmed at the manufacturing stagewith the cable data). Alternatively, memory 37A is another type of othermemory.

Typically, the cable data are indicative of all or some of the cablemanufacturer, the cable type and/or cable class, a date code, afrequency-dependent attenuation table, FEXT (far-end crosstalk)coefficients, cable impedance, cable length (electrical length), cablegrade, EMI-related coefficients, common mode radiation, cable speed,intra pair skew, and other information.

In FIG. 3, memory 47A (coupled to serial device 47) stores cable data inaccordance with the invention. Memory 47A is preferably implemented as aROM.

Each of serial devices 60 and 61 (of FIG. 4) and 77 (of FIG. 5) alsoincludes a memory (preferably a ROM) which stores cable data inaccordance with the invention. In variations on cable 32, 52, or 72, thecable's serial device (e.g., a serial device that replaces serial device37, 47, or 77) does not include a memory which stores cable data, butthe cable does include such a memory (in one of its connectors) that isdistinct from and coupled to the cable's serial device.

Each of cables 32, 42, and 52 is an intelligent cable in the sense thatit includes a built-in active serial device (typically implemented as anintegrated semiconductor circuit) configured to respond to a request forcable data stored in the cable. Each on-cable serial device (e.g.,device 37, 47, 60, or 61) can be implemented using commerciallyavailable technology (e.g., as a commercially available module ormodified version of such a module).

Conventionally, the DDC channel of a DVI link is used to transmit anExtended Display Identification (“EDID”) message from a monitorassociated with a receiver to a transmitter, and to transmit controlsignals for the monitor from the transmitter. The EDID message specifiesvarious characteristics of the monitor. In the FIG. 2 system, devices 38and 39 are configured to perform these conventional operations. Forexample, device 38 is configured to assert an EDID request over the DDCchannel to device 39, and device 39 is configured to respond to suchrequest by transmitting an EDID message to device 38 over the DDCchannel. The I2C protocol allows several serial devices to be connectedalong one pair of conductors, and allows an I2C master device (e.g.,device 38) to communicate with any desired one of such serial devices.Thus, in accordance with the invention, device 38 is configured to querydevice 39 to determine whether receiver 33 has equalization capability(and device 39 is configured to respond to such a query), and device 38is also configured to assert to device 37 a request for cable datastored in cable 32 (and device 37 is configured to respond to such arequest).

In the systems of FIGS. 3 and 4, devices 48, 49, 58, and 59 areconfigured to perform the conventional DDC channel operations describedin the previous paragraph. In accordance with the invention, device 48is also configured to query device 49 to determine whether receiver 43has equalization capability (and device 49 is configured to respond tosuch a query), device 48 is configured to assert to device 47 a requestfor cable data stored in cable 42 (and device 47 is configured torespond to such a request by asserting cable data from memory 47A todevice 48 in serial fashion over one or both of the DDC CLK and DDC DATAlines), device 58 is configured to query device 59 to determine whetherreceiver 53 has equalization capability (and device 59 is configured torespond to such a query), and device 58 is configured to assert todevice 60 or 61 a request for cable data stored in cable 52 (and therelevant one of devices 60 and 61 is configured to respond to such arequest by asserting cable data to device 58 in serial fashion over oneor both of the DDC CLK and DDC DATA lines).

In other embodiments, the inventive cable is used to implement a linkthat is not a DVI link but does include a DDC channel, and its conductorset includes Display Data Channel (“DDC”) lines for implementing the DDCchannel. Preferably, the cable includes a serial device configured torespond to a request for cable data (received on at least one of the DDClines) by asserting cable data (accessed from a memory in the cable) toat least one of the DDC lines (e.g., for transmission in serial fashionto an external device coupled to the DDC lines).

One respect in which the FIG. 3 system differs from the FIG. 2 system isthat cable 42 includes equalization network 50, while cable 32 of FIG. 2does not include equalization circuitry. Network 50 includes anequalization filter for each of the video data channels (conductors“Red,” “Green,” and “Blue”) and the pixel clock channel (the conductorpair labeled “Clock”). Equalization network 50 is typically implementedas passive circuitry. Preferably, the cable data stored in memory 47A ofcable 42 includes equalization data indicating that cable 42 is equippedwith equalization network 50 and indicating at least one characteristicor parameter of equalization network 50. Device 47 is preferablyconfigured to respond to a cable data request from device 48 bytransmitting the equalization data to device 48 in serial fashion overthe DDC channel. Transmitter 41 is preferably configured to use theequalization data as an input in its own determination as to whether toequalize the data and clock signals to be transmitted over the videodata and pixel clock channels and if so what equalization to apply tosuch data and clock signals. For example, transmitter 41 can use theequalization data from cable 52 to choose pre-emphasis values that willnot result in over-equalization of the data and clock signals receivedat receiver 43 after transmission over the video data and pixel clockchannels (and undergoing equalization in network 50).

An equalization network in the cable (e.g., equalization network 50) canbe useful for reducing dispersion and reflection. In the case of signaltransmission over a very long cable, the transmitter would typicallyactively boost the signal to be transmitted to mitigate expected lossduring transmission, and would typically also de-skew each differentialsignal transmitted over the cable (e.g., the differential signaltransmitted over each of the conductor pairs labeled “Red,” “Green,”“Blue,” and “Clock” in the system of FIG. 2, 3, 4, or 5) to mitigateintra pair skews.

The FIG. 4 system differs from the FIG. 2 in several respects: cable 52of FIG. 4 includes two serial devices (60 and 61) rather than one; eachserial device of cable 52 is coupled to a light-emitting diode (LED);transmitter 51 includes LED 65 (transmitter 31 includes no LED); andreceiver 53 includes LED 64 (receiver 33 includes no LED). LED 62 ofcable 52 is coupled to and driven by serial device 60, and LED 63 ofcable 52 is coupled to and driven by serial device 61. In variations onthe FIG. 4 system at least one of the LEDs is replaced by aradiation-emitting element of another type.

In FIG. 4, device 60 is preferably configured to generate drivingsignals for LED 62 by translating commands received over the DDC channelfrom device 58 in transmitter 51. Device 61 is preferably configured togenerate driving signals for LED 63 by translating commands receivedover the DDC channel from device 59 in receiver 53 or from device 58 intransmitter 51. In response to the driving signals, LEDs 60 and 61 emitradiation having a desired appropriate color, brightness, and/orblinking pattern. The driving signals asserted by serial device 60 cancause LED 62 to emit radiation indicative of connection status (e.g.,whether connector 54 is properly connected to transmitter 51), or numberof errors, or other information (e.g., other information for diagnosingsignal transmission status or status of cable 52). The driving signalsasserted by serial device 61 can cause LED 63 to emit radiationindicative of connection status (e.g., whether connector 56 is properlyconnected to receiver 53), or number of errors, or other information(e.g., other information for diagnosing signal transmission or status ofcable 52).

In the FIG. 4 system, transmitter 51 includes circuitry for driving LED65, and receiver 53 includes circuitry for driving LED 64. Preferably,transmitter 51 is configured to drive LED 65 such that the color,brightness and/or blinking pattern of radiation emitted from LED 65 isuseful for guiding cable installation or checkup of connections (e.g.,the radiation is indicative of whether cable 52 is connected to one orboth of transmitter 51 and receiver 53). Preferably, receiver 53 isconfigured to drive LED 64 such that the color, brightness and/orblinking pattern of radiation emitted from LED 64 is useful for guidingcable installation or checkup of connections (e.g., the radiation isindicative of whether cable 52 is connected to one or both oftransmitter 51 and receiver 53).

The color, brightness and/or blinking pattern of radiation emitted fromall or some of LEDs 62, 63, 64, and 65 can also indicate the type ofsignal (or types of signals) being transmitted through cable 52 (e.g.,whether the signal is a digital signal, content protected signal, oraudio signal) and/or can indicate specific signal activities.

The color, brightness and/or blinking pattern of radiation emitted fromLED 62 and/or 63 can change in response to the data itself (i.e., inresponse to the data being transmitted from transmitter 51 to receiver53). Preferably, serial device 58 in transmitter 51 or device 59 inreceiver 53 asserts (via the DDC channel) signals indicative of specificinformation regarding the data, and serial device 60 and/or 61translates such signals into LED-driving signals.

An example of how the color, brightness, or blinking pattern ofradiation emitted from LED 62, 63, 64, and/or 65 can be used is forcable management and debugging of cable problems in systems that employmany cables (e.g., a system in a typical studio, in which multiplecables are connected between multiple devices and in which multiplecables can be connected between two devices). In such systems,connecting appropriate cables to the proper devices and keeping track ofthe cables' connections can be difficult tasks. An LED in each cablethat corresponds to a device pair can emit a specific color or on/offlight pattern, and an LED in each device that corresponds to a cable canemit a specific color and/or pattern. When such LEDs are available, theuser only needs to check cables that emit (or fail to emit) specificradiation to determine ‘error’ status. Or, the user can match alldevices and cables that display a specific color and/or blinking lightpattern.

If LED 62 and/or LED 63 is implemented as a multiple-color LED, thecircuitry for controlling LED 62 and/or LED 63 (to cause them to emitradiation indicative of signal type and/or signal activity) can beimplemented more simply.

We next describe the system of FIG. 5 which includes transmitter 71,receiver 73, and cable 72 coupled between transmitter 71 and receiver73. The elements of FIG. 5 that are identical to corresponding elementsof FIG. 2 are numbered identically in FIGS. 2 and 5 and the foregoingdescription of them will not be repeated. Transmitter 71 includes cipherengine 88 and encoder/serializer circuitry 89 (for encoding encrypteddata generated by cipher engine 88, serializing the encoded, encrypteddata, and transmitting the serialized data). Receiver 73 includesdeserializer/decoder circuitry 99 (for decoding and deserializingencoded, encrypted data received from cable 72) and cipher engine 98 fordecrypting the decoded data output from circuitry 99). Serial device 77of cable 72 is configured to perform all the operations performed byserial device 37 of FIG. 2 and includes a memory for storing cable data.In preferred implementations, the cable data stored in device 77 includedata indicative of whether cable 72 is a secure cable over whichtransmitter 71 can securely transmitted encrypted data, and transmitter71 is configured not to transmit encrypted data to cable 72 unless anduntil transmitter 71 receives cable data indicating that cable 72 is asecure cable.

In other preferred implementations, device 77 stores a cryptographic keyset. In implementations of this type, a different cryptographic key setis preferably stored in each of cipher engine 88, cipher engine 98, andcable 72, and device 77 is configured to execute a verificationoperation with transmitter 71 over the DDC channel. In this verificationoperation, transmitter 71 and device 77 identify themselves (this steptypically includes an exchange of keys) and transmitter 77 determineswhether cable 72 is a secure digital cable. Transmitter 71 would alsoperform another verification operation directly with receiver 73 (e.g.,a conventional verification operation performed over the DDC channel).Upon successful completion of verification operations with both receiver73 and serial device 77, transmitter 71 would transmit encrypted data tocable 72, and the encrypted data would propagate through cable toreceiver 73 and undergo decryption in cipher engine 79.

In a class of embodiments, cipher engines 88 and 98 and device 77operate in accordance with the HDCP protocol, and each stores an HDCPkey set. During operation of such embodiments of the FIG. 5 system(before transmission of encrypted data by transmitter 71), transmitter71 would perform a verification operation with each of device 77 andreceiver 73, and would not transmit encrypted data to cable 72 untilafter successfully completing both verification operations. Theverification operation between transmitter 71 and receiver 73 could be aconventional HDCP verification operation. The verification operationbetween transmitter 71 and device 77 could also be a conventional HDCPverification operation, or it could be a modified version ofconventional HDCP verification operation. The HDCP key set stored in thetransmitter would include at least some keys unique to the transmitter(or to a small number of devices including the transmitter), the HDCPkey set stored in the receiver would include at least some keys uniqueto the receiver (or to a small number of devices including thereceiver), and the HDCP key set stored in the cable would include atleast some keys unique to the cable (or to a small number of devicesincluding the cable).

In any of the described embodiments, the serial bus master in thetransmitter (serial device 38, 48, 58, or 78) is preferably configuredto obtain cable data (by communicating with the serial device in thecable) as soon as the cable is attached to the transmitter. The serialbus master in the transmitter is preferably also configured to query aserial device in the receiver (device 39, 49, 59, or 79) to determinewhether the receiver has equalization capability, and the serial devicein the receiver is configured to assert receiver data (indicative of thereceiver's equalization capability) serially to the transmitter inresponse to such a query. The transmitter is preferably configured touse the cable data and the receiver data obtained from the cable andreceiver to perform at least one (and preferably all) of the followingoperations:

determining optimal pre-emphasis values for equalizing data and clocksignals in the transmitter before the data and clock signals aretransmitted over the cable, and determining optimal receiverequalization values (for equalization of data and clock signals in thereceiver), both assuming a specific rate of data transmission over thecable to the receiver;

sending equalization data and/or control bits to the receiver to set (orcause the receiver to set) at least one parameter of equalizationcircuitry in the receiver (e.g., equalization circuitry indeserializer/decoder circuitry 99 of receiver 73 of FIG. 5). Forexample, the transmitter can transmit at least some of the cable data(and/or control bits generated in response to the cable data) to thereceiver for use by the receiver to set at least one equalizationparameter;

skewing video data (e.g., RGB data) to be transmitted over the cable tominimize crosstalk;

skewing the two components of at least one differential signaltransmitted over a conductor pair of the cable to minimize EMI and intrapair skews that result during transmission (e.g., skewing the twocomponents of the differential signal transmitted over each of theconductor pairs labeled “Red,” “Green,” “Blue,” and “Clock” in thesystem of FIG. 2, 3, 4, or 5); and

sending data or control bits to the receiver to set (or cause thereceiver to set) at least one parameter of termination circuitry in thereceiver (e.g., termination circuitry in deserializer/decoder circuitry99 of receiver 73 of FIG. 5). For example, the transmitter could sendcontrol bits to the receiver to direct the receiver to adjust theimpedance of a termination coupled to each of the conductor pairslabeled “Red,” “Green,” “Blue,” and “Clock” in the system of FIG. 2, 3,4, or 5, to terminate each conductor of each such conductor pair with aspecific impedance.

In a class of embodiments, the inventive cable includes a subsystemconfigured to assert information (e.g., by displaying an indication ofcable guide information) to a user or external device. In some suchembodiments, the cable implements at least one cable guide function byasserting cable guide information (e.g., by displaying an indication ofthe cable guide information) to a user or external device. For example,the cable guide information can indicate what type of device a free endof the cable should be connected to when the other end of the cable hasbeen connected to a device of known type. In some such embodiments,circuitry in the cable causes the cable to display an indication of thetype of device to which the free end should be connected when thecircuitry has determined that the other end of the cable has beenconnected to a device of known type.

In a typical embodiment in this class, when one end of the cable isconnected to a device, circuitry (e.g., a serial device) within thecable determines what device the cable is connected to, andautomatically indicates what device the other end of the cable should beconnected to. For example, the cable displays an indication of the typeof device to which the free end of the cable should be connected, e.g.,by causing an LED in the cable to emit radiation indicating thisinformation. If the target device (to which the free end of the cableshould be connected) is configured to display a matching indication(identifying the connector of the target device that should receive thecable), the user just needs to find the matching indication (e.g., thesame colored glow) near one of the connectors of the target device(which may be one of many audio-visual devices mounted on a rack) andconnect the free end of the cable to that connector.

Embodiments in this class can be implemented to rely on an externaldevice (coupled to the cable) to supply power to the circuitry withinthe cable. Alternatively, the inventive cable could include its ownpower supply for supplying power to the serial device or other circuitrywithin the cable. In typical display systems in which a cable isconnected between a display device (e.g., a monitor) at one end of thecable, and a host, computer, set-top box, or similar device at the otherend of the cable, power supplies in the devices at both ends of thecable are coupled to power lines within the cable. For example, the HotPlug Detect (HPD) line of a DVI/HDMI standard cable is powered by themonitor (or other display device) to which the cable is connected, andthe DDC power lines of such a cable are powered by the host (or computeror set-top box) to which the other end of the cable is connected.

Cable 82, coupled between transmitter 51 and receiver 53 of FIG. 6, isan example of the embodiments discussed in the three precedingparagraphs. Transmitter 51 and receiver 53 of FIG. 6 are identical totransmitter 51 and receiver 53 of FIG. 4. Elements of cable 82 that areidentical to corresponding elements of cable 52 of FIG. 4 areidentically numbered in FIGS. 4 and 6. Cable 82 differs from cable 52 inthat connector 84 of cable 82 includes LED drive circuit 85 (coupled toDDC power lines “VCC” and “GND” of cable 82 and to each of LED 62 andLED 63) rather than serial device 60 of FIG. 4, and in that connector 86of cable 82 includes LED drive circuit 87 (coupled to the HPD line andthe DDC ground line “GND” of cable 82 and to each of LED 62 and LED 63)rather than serial device 61 of FIG. 4. In variations on the FIG. 6embodiment, circuit 87 and LED 63 are omitted) or circuit 85 and LED 62are omitted.

LED drive circuits 85 and 87 of FIG. 6 do not communicate withtransmitter 51 or receiver 53 via any of conductors 55. Instead, LEDdrive circuit 85 monitors DDC power lines within cable 82 to determinewhen cable 82 is coupled to a device that maintains at least apredetermined minimum voltage between the DDC power lines. The presenceof such minimum voltage between the DDC power lines indicates thatconnector 84 or 86 is connected to a transmitter (because power isalways supplied to the DDC channel of a DVI link by a transmitter).Circuit 85 causes LED 62 and LED 63 to display an indication that thefree end of cable 82 should be connected to the DVI connector of adisplay device in response to determining that the voltage between theDDC power lines exceeds the minimum voltage.

LED drive circuit 87 monitors the electric potential of the Hot PlugDetect (HPD) line within cable 82 (the HPD line is shown in FIG. 6, andis not shown but present in each of cables 32, 42, 52, and 72 of FIGS.2, 3, 4, and 5) to determine when cable 82 is coupled to a device thatmaintains at least a predetermined minimum potential on the HDP line(i.e., a predetermined minimum voltage between the HPD line and areference potential). The presence of the minimum potential on the HPDline indicates that connector 84 or 86 is connected to a receiver(because power is always supplied to the HPD line of a DVI link by areceiver, which is typically a display device). Circuit 87 thus causesLED 62 and LED 63 to display an indication that the free end of cable 82should be connected to the DVI connector of a video source (e.g., ahost, computer, or set-top box) in response to determining that theelectric potential of the HPD line exceeds the minimum potential.

In the FIG. 6 embodiment, each of circuits 85 and 87 consumes power froma device (transmitter 51 or receiver 53) coupled to cable 82 as requiredto determine whether to drive LEDs 62 and 63, and to drive the LEDs atappropriate times. In other embodiments of the invention, the inventivecable includes its own power supply for supplying the power needed todisplay (or otherwise assert to a user or an external device)appropriate cable guide information and to determine when to assert thecable guide information.

In variations on the FIG. 6 embodiment, circuitry within the inventivecable, upon determining that a device is coupled to one end of thecable, causes the cable to display an indication of the type of deviceto which the connector at the cable's other end should be connected. Forexample, in some such embodiments, if the circuitry detects that the HPDline is powered up, it knows that one end of the cable is connected to aspecific type of connector (e.g., a DVI connector) of a display device,and displays an indication that the other end of the cable should beconnected to a specific type of connector (e.g., a DVI connector) of ahost (or computer or set-top box). If the circuitry determines that DDCpower is on, it knows that one end of the cable is connected to a host(or computer or set-top box) and displays an indication that the otherend of the cable should be connected to a specific type of connector(e.g., a DVI connector) of a display device. The circuitry can cause anLED at one end (or at each of both ends) of the cable to emit radiationindicating that the free end of the cable should be coupled to a deviceof an indicated type (e.g., a type indicated by emitted radiation), orcan cause any other indicating means in the cable to indicate (e.g., byemitting radiation) that the free end should be coupled to a device ofan indicated type. Optionally, circuitry within the cable can cause LEDs(or any other indicating means) at both ends of the cable to emitradiation indicating (or otherwise to indicate) whether each end is orshould be coupled to a device of an indicated type.

In some embodiments, the cable displays an indication at only one end ofthe cable (or displays different indications at different ends of thecable), but this requires more sophistication in the detection scheme.Embodiments which display the same indication at both ends of the cable(e.g., cable 82 of FIG. 6) are typically simpler to implement.

The serial device (or other circuitry) within the inventive cable candisplay cable guide information (or other information) in any of variousways. For example, the circuitry can cause an LED to blink when only oneend of the cable is hooked up, and when both ends of the cable have beenproperly connected, the circuitry can cause the LED to emit steady lightto indicate successful connection of both ends. Alternatively, thecircuitry can change the color of display or brightness of the displayto indicate appropriate cable guide information. Display of cable guideinformation in accordance with the invention can be useful if the cablecan be fit into various very similar but not compatible connectors. Whenthe cable has not been connected to the proper connector of a device towhich it is supposed to be connected, the cable should not indicate a“successful connection” signal. Optionally, even when the cable has beenconnected to the correct connector of the correct device, if theconnection is not proper in some electrical or mechanical sense, thecable does not indicate a successful connection signal. Thisfunctionality can reduce user frustration significantly when acomplicated system does not work properly and the user is faced with thetask of finding out what went wrong during establishment of acomplicated web of connections.

In variations on embodiments described above, the inventive cable storescable data other than in a ROM. For example, in some embodiments theinventive cable stores cable data in registers or other writable memory(e.g., a memory to which an external device can write new data tosupplement previously-stored cable data, or to which an external devicecan write updated cable data to replace previously-stored cable data).

In other embodiments (e.g., the embodiment to be described withreference to FIG. 7), the inventive cable includes an analog memorywhich stores cable data. Cable 92 of FIG. 7 differs from cable 42 ofFIG. 3 in that it lacks equalization network 50, serial device 47, andmemory 47A, and instead includes analog memory 97. Analog memory 97stores cable data (in a sense to be described), is coupled to DDC powerlines “VCC” and “GND” of cable 92, and can be implemented as a resistoror resistor network. When the cable is connected to a device(transmitter 91 or receiver 93), analog circuitry (not specificallyshown in FIG. 7) within the device is coupled via the DDC power lines toanalog memory 97. The analog circuitry “reads” the cable data frommemory 97 by generating or measuring a current (or other electricalsignal) indicative of the cable data in response to asserting apredetermined voltage across the DDC power lines “VCC” and “GND.” Thiscurrent (or other electrical signal) is determined by a resistance (orratio of resistances) that is in turn determined by the resistor orresistors that comprise analog memory 97.

In another class of embodiments, the invention is a method for providingcable data stored in a cable to an external device, including the stepsof asserting a request from the external device to at least oneconductor of the cable; and responding to the request by accessing atleast some of the cable data and transmitting the accessed cable dataserially from the cable to the external device on at least one conductorof the cable. When the external device is a transmitter configured toapply pre-emphasis to content data, the method can also include the stepof determining pre-emphasis values for use in applying pre-emphasis tothe content data in response to at least some of the cable data receivedfrom the cable. When the external device is a transmitter configured totransmit data over the cable to a receiver, and the receiver isconfigured to perform equalization on the data, the method can alsoinclude the steps of setting at least one said equalization parameter inresponse to at least some of the cable data received at the transmitterfrom the cable; and in the receiver, performing equalization on the datain accordance with the at least one equalization parameter. When theexternal device is a transmitter configured to transmit data over thecable to a receiver having termination circuitry, the method can alsoinclude the step of configuring the termination circuitry in response toat least some of the cable data received at the transmitter from thecable.

In another class of embodiments, the invention is a method for assertingcable guide information from a cable including a conductor set and aninformation asserting subsystem, said method including the steps of: (a)monitoring at least one conductor of the conductor set; and (b) inresponse to a change in state of at least one conductor of the conductorset, asserting the cable guide information from the informationasserting subsystem. In some embodiments, step (b) includes the step ofemitting radiation indicative of the cable guide information in responseto a change in state of said at least one conductor of the conductor setindicating that a device is coupled to the cable. In some embodiments,step (b) includes the step of emitting radiation indicative of the cableguide information in response to a change in state of said at least oneconductor of the conductor set indicating that a device of a first typeis coupled to the cable, where the cable guide information is indicativeof a second type of device to which a free end of the cable should beconnected.

When the cable includes a conductor set, the external device is atransmitter configured to transmit data over the cable to a receiver,and the request is asserted from the transmitter to a first conductorsubset of the conductor set and the accessed cable data are transmittedto the external device over the first conductor subset, the method canalso include the step of transmitting content data from the transmitterto the receiver over a second conductor subset of the conductor set.When the cable includes Display Data Channel lines and other conductors,the external device is a transmitter configured to transmit data overthe cable to a receiver, the request is asserted from the transmitter toat least one of the Display Data Channel lines and the accessed cabledata are transmitted to the external device over at least one of theDisplay Data Channel lines, the method can also include the step oftransmitting content data from the transmitter to the receiver over atleast one of the other conductors.

When the cable includes a radiation-emitting element, the method canalso include the steps of asserting commands from the external device tothe cable on at least one conductor of the cable, and in response to thecommands, operating circuitry in the cable to generate driving signalsfor the radiation-emitting element, and optionally also emittingradiation from the radiation-emitting element in response to the drivingsignals such that the radiation has at least one of a color, brightness,and blinking pattern determined by at least one of the commands.

When the external device is a transmitter and the cable stores acryptographic key set, the method can also include the step of operatingcircuitry in the cable to execute a verification operation with thetransmitter including by transmitting at least one cryptographic key ofthe key set over at least one conductor of the cable to the transmitter.

It should be understood that while some embodiments of the presentinvention are illustrated and described herein, the invention is definedby the claims and is not to be limited to the specific embodimentsdescribed and shown.

1. A cable, including: a conductor set; and a subsystem, coupled to atleast one conductor of the conductor set, and configured to respond to achange in state of at least one conductor of the conductor set byasserting cable guide information wherein the subsystem includes: atleast one radiation-emitting element; and circuitry coupled to andcapable of driving the radiation-emitting element, wherein the circuitryis configured to determine from the change in state of the at least oneconductor whether a device of a first type is coupled to the cable andto cause the radiation-emitting element to emit radiation indicative ofthe cable guide information in response to determining that a device ofsaid first type is coupled to the cable, wherein the cable guideinformation is indicative of a second type of device to which a free endof the cable should be connected.
 2. The cable of claim 1, wherein theradiation-emitting element is an LED.
 3. A cable, including: a conductorset; and a subsystem, coupled to at least one conductor of the conductorset, and configured to respond to a change in state of at least oneconductor of the conductor set by asserting cable guide information,wherein the subsystem includes: at least one radiation-emitting element;a first circuit coupled to and capable of driving the radiation-emittingelement, wherein the first circuit is configured to determine from achange in state of a first subset of the conductor set whether a deviceof a first type is coupled to the cable and to cause theradiation-emitting element to emit radiation indicating that a device ofa second type should be connected to the cable in response todetermining that a device of the first type is coupled to the cable; anda second circuit coupled to and capable of driving theradiation-emitting element, wherein the second circuit is configured todetermine from a change in state of a second subset of the conductor setwhether a device of the second type is coupled to the cable and to causethe radiation-emitting element to emit radiation indicating that adevice of the first type should be connected to the cable in response todetermining that a device of the second type is coupled to the cable. 4.A method for providing cable data stored in a cable to an externaldevice, including the steps of: asserting a request from the externaldevice to at least one conductor of the cable; responding to the requestby accessing at least some of the cable data and transmitting theaccessed cable data serially from the cable to the external device on atleast one conductor of the cable, wherein the external device is atransmitter configured to apply pre-emphasis to content data; anddetermining pre-emphasis values for use in applying pre-emphasis to thecontent data in response to at least some of the cable data receivedfrom the cable.
 5. A method for providing cable data stored in a cableto an external device, including the steps of: asserting a request fromthe external device to at least one conductor of the cable; respondingto the request by accessing at least some of the cable data andtransmitting the accessed cable data serially from the cable to theexternal device on at least one conductor of the cable, wherein theexternal device is a transmitter configured to transmit data over thecable to a receiver, and the receiver is configured to performequalization on the data; setting at least one said equalizationparameter in response to at least some of the cable data received at thetransmitter from the cable; and in the receiver, performing equalizationon the data in accordance with the at least one equalization parameter.6. A method for providing cable data stored in a cable to an externaldevice, including the steps of: asserting a request from the externaldevice to at least one conductor of the cable; responding to the requestby accessing at least some of the cable data and transmitting theaccessed cable data serially from the cable to the external device on atleast one conductor of the cable, wherein the external device is atransmitter configured to transmit data over the cable to a receiverhaving termination circuitry, and also including the step of:configuring the termination circuitry in response to at least some ofthe cable data received at the transmitter from the cable.
 7. A methodfor providing cable data stored in a cable to an external device,including the steps of: asserting a request from the external device toat least one conductor of the cable; and responding to the request byaccessing at least some of the cable data and transmitting the accessedcable data serially from the cable to the external device on at leastone conductor of the cable, wherein the cable includes a conductor set,the external device is a transmitter configured to transmit data overthe cable to a receiver, the request is asserted from the transmitter toa first conductor subset of the conductor set and the accessed cabledata are transmitted to the external device over the first conductorsubset, and also including the step of: transmitting content data fromthe transmitter to the receiver over a second conductor subset of theconductor set.
 8. A method for providing cable data stored in a cable toan external device, including the steps of: asserting a request from theexternal device to at least one conductor of the cable; responding tothe request by accessing at least some of the cable data andtransmitting the accessed cable data serially from the cable to theexternal device on at least one conductor of the cable, wherein thecable includes Display Data Channel lines and other conductors, theexternal device is a transmitter configured to transmit data over thecable to a receiver, the request is asserted from the transmitter to atleast one of the Display Data Channel lines and the accessed cable dataare transmitted to the external device over at least one of the DisplayData Channel lines, and also including the step of: transmitting contentdata from the transmitter to the receiver over at least one of the otherconductors.
 9. A method for providing cable data stored in a cable to anexternal device, including the steps of: asserting a request from theexternal device to at least one conductor of the cable; responding tothe request by accessing at least some of the cable data andtransmitting the accessed cable data serially from the cable to theexternal device on at least one conductor of the cable, wherein theexternal device is a transmitter, the cable stores a cryptographic keyset, and also including the step of: operating circuitry in the cable toexecute a verification operation with the transmitter including bytransmitting at least one cryptographic key of the key set over at leastone conductor of the cable to the transmitter.
 10. A method forasserting cable guide information from a cable including a conductor setand an information asserting subsystem, said method including the stepsof: (a) monitoring at least one conductor of the conductor set; and (b)in response to a change in state of at least one conductor of theconductor set, asserting the cable guide information from theinformation asserting subsystem, wherein step (b) includes the step of:in response to a change in state of said at least one conductor of theconductor set indicating that a device of a first type is coupled to thecable, emitting radiation indicative of the cable guide information,wherein the cable guide information is indicative of a second type ofdevice to which a free end of the cable should be connected.